256 



of less depth, and, becoming only covered with a moderately thick 

 coat, would become peat bogs ; and, if left for a long series 

 of time totally undisturbed, would, perhaps, form lakes of petro- 

 leum, similar to that which now exists in the island of Trinidad, a 

 description of which has been already given in the Fourteenth 

 Letter. 



When we reflect on the situation of coal, and of the various 

 strata which are interposed between its several beds ; it must, how- 

 ever, be admitted that considerable difficulties still oppose the satis- 

 factory explanation of these phenomena. Among these, not the 

 least is the frequent alternation of coal and lime-stone, and which 

 undoubtedly best agrees with the idea of immense lakes of sea or 

 fresh water undergoing alternate fillings and emptyings : in the 

 former state, depositing strata of stone, and in the latter, forming 

 beds of decomposing vegetable matter. 



Yours, &c. 



LETTER XXV. 



INQUIRY WHETHER THE VEGETABLE MATTER WAS DEPOSITED 

 AT THE DELUGE UNDER CIRCUMSTANCES FAVOURABLE TO ITS 

 CONVERSION TO COAL.. ..BITUMEN ALONE NOT FITTED FOR 

 FUEL. ...OTHER MATTERS NECESSARY TO BE ADDED. ...PECULIAR 

 ARRANGEMENT OF THE PARTICLES. 



THE next question which demands consideration is, whether such 

 an arrangement of the materials of the flooded surface of the ante- 

 diluvian world, as has been assumed in my last Letter, would be 



